Semiconductor light emitting device with stacked light emitting elements

ABSTRACT

A light emitting device which can be easily manufactured and can control the positions of light emission precisely, and an optical device. A first and second light emitting elements are formed on one face of a supporting base. The first light emitting element has an active layer made of GaInN mixed crystal on a GaN-made first substrate on the side thereof on which the supporting base is disposed. The second light emitting element has lasing portions on a GaAs-made second substrate on the side thereof on which the supporting base is disposed. Since the first and second light emitting elements are not grown on the same substrate, a multiple-wavelength laser having the output wavelength of around 400 nm can be easily obtained. Since the first substrate is transparent in the visible region, the positions of light emitting regions in the first and second light emitting elements can be precisely controlled by lithography.

This application is a continuation of Ser. No. 09/783,914, filed Feb.15, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting device having aplurality of light emitting elements, and an optical device using thesame.

2. Description of the Related Art

In recent years, in the field of light emitting devices, a semiconductorlaser (LD; laser diode) in which a plurality of light emitting portionsof different output wavelengths are formed on the same substrate (orboard) (hereinafter referred to as a multiple-wavelength laser) isactively developed. An example of such a multiple-wavelength laser is,as shown in FIG. 1, obtained by forming a plurality of light emittingportions of different output wavelengths on a single chip (what iscalled a monolithic type multiple-wavelength laser). In themultiple-wavelength laser, for example, a lasing portion 201 formed bygrowing layers of semiconductor materials of the system AlGaAs by vaporphase epitaxy and a lasing portion 202 formed by growing layers ofsemiconductor materials of the system AlGaInP are disposed side by sideon one face of a substrate 212 made of GaAs (gallium arsenide) with anisolation groove 211 between them. In this case, the output wavelengthof the lasing portion 201 is in the range of the order of 700 nm (forexample, 780 nm) and that of the lasing portion 202 is in the range ofthe order of 600 nm (for example, 650 nm).

Except for the structure shown in FIG. 1, a structure (what is called ahybrid type multiple-wavelength laser) in which a plurality ofsemiconductor lasers LD₁ and LD₂ having different output wavelengths aremounted side by side on a board 221 has been also proposed. Theabove-mentioned monolithic-type laser is, however, more effective incontrolling the light emitting point intervals with high accuracy.

These multiple-wavelength lasers are used, for example, as laser lightsources of optical disk drives. At present, in an optical disk drive,semiconductor laser light in the range of the order of 700 nm isgenerally used for optical playback of CD (Compact Disk) recording orfor optical recording/playback using recordable optical disks such asCD-Rs (recordable CDs), CD-RWs (rewritable CDs) or MDs (Mini Disks).Semiconductor laser light in the range of the order of 600 nm is usedfor optical recording/playback using DVDs (Digital Versatile Disks). Bymounting a multiple-wavelength laser as described above on an opticaldisk drive, optical recording/playback becomes possible with respect toany existing optical disks. Moreover, the lasing portions 201 and 202are disposed side by side on the same substrate (as for thesemiconductor lasers LD₁ and LD₂ of the hybrid type, on the same board),only one package is necessary for the laser light source. The number ofparts of an optical system such as an objective lens and a beam splitterfor optical recording/playback using various optical disks is decreasedto simplify the configuration of the optical system. Thus, reduction insize and cost of an optical disk drive can be achieved.

Meanwhile, in recent years, the demand for further growth of opticalrecording area density by using semiconductor lasers of shorter outputwavelengths has been growing. Heretofore known materials ofsemiconductor lasers addressing the demand are Group III-V compoundsemiconductors of the nitride system (hereinbelow, also calledsemiconductors of the system GaN) typified by GaN, AlGaN mixed crystals,and GaInN mixed crystals. Semiconductor lasers using semiconductors ofthe system GaN are capable of light emission at a wavelength of around400 nm, which is regarded as the limit wavelength at which opticalrecording/playback is done using an optical disk and an existing opticalsystem, and therefore, they receive much attention as light sources ofnext-generation optical recording/playback apparatuses. It is alsoexpected as light sources of full-color displays using three primarycolors of RGB. Thus, development of multiple-wavelength lasers withlasing portions of the system GaN is desired.

As an example of related-art multiple-wavelength lasers with lasingportions of the system GaN, as shown in FIG. 3, a multiple-wavelengthlaser is proposed in which the lasing portion 201 of the system AlGaAs,the lasing portion 202 of the system AlGaInP, and the lasing portion 203of the system GaN are formed side by side on one face of a substrate 231made of SiC (silicon carbide) with isolation grooves 211 a and 211 bbetween them (refer to Publication of Japanese Unexamined PatentApplication No. Hei-11-186651).

In the case of fabricating the monolithic type multiple-wavelengthlaser, however, there is a problem such that it is difficult tointegrate lasing portions on the same substrate as one chip due to, forexample, a large difference in lattice constant between the materials ofthe system GaN and the materials of the system AlGaAs or AlGaInP.

The hybrid type multiple-wavelength laser has, as already described, aproblem of poor controllability on the light emitting point intervals.The side-by-side arrangement of three or more semiconductor laserscauses an inconvenience such that the controllability on the lightemitting point intervals further deteriorates.

SUMMARY OF THE INVENTION

The invention has been achieved in consideration of the problems and itsobject is to provide a light emitting device which can be easilymanufactured and can control the position of light emission withaccuracy, and an optical device using the light emitting device.

A light emitting device according to the invention has a plurality oflight emitting devices stacked on one face of a supporting base

Another light emitting device according to the invention has: asupporting base; a first light emitting element having a firstsubstrate, provided on one face of the supporting base; and a secondlight emitting element having a second substrate, provided on the sideof the first light emitting element opposite to the supporting base.

An optical device according to the invention has a light emitting devicein which a plurality of light emitting elements are stacked on one faceof a supporting base.

In another optical device according to the invention, a light emittingdevice is mounted. The light emitting device comprises: a supportingbase; a first light emitting element having a first substrate, providedon one face of the supporting base; and a second light emitting elementhaving a second substrate, provided on the side of the first lightemitting element opposite to the supporting base.

In the light emitting device according to the invention and the otherlight emitting device according to the invention, a plurality of lightemitting elements are stacked on one face of a supporting base.Therefore, the devices are easily manufactured and the light emittingregions are disposed with high precision.

In the optical device according to the invention and the other opticaldevice according to the invention, they have the light emitting deviceaccording to the invention in which light emitting regions are disposedwith high precision. This contributes to size reduction.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section showing an example of the configuration of arelated-art light emitting device.

FIG. 2 is a cross section showing another example of the configurationof a related-art light emitting device.

FIG. 3 is a cross section showing still another example of theconfiguration of a related-art light emitting device.

FIG. 4 is a cross section showing the configuration of a light emittingdevice according to a first embodiment of the invention.

FIG. 5 is a partly-exploded perspective view showing the configurationof a package in which the light emitting device shown in FIG. 4 isenclosed.

FIGS. 6A and 6B are cross sections for explaining a method ofmanufacturing the light emitting device shown in FIG. 4.

FIGS. 7A and 7B are cross sections for explaining a manufacturingprocess subsequent to FIG. 6B.

FIGS. 8A and 8B are cross sections for explaining a manufacturingprocess subsequent to FIG. 7B.

FIGS. 9A and 9B are cross sections for explaining a manufacturingprocess subsequent to FIG. 8B.

FIG. 10 is a diagram showing the configuration of an optical diskrecording/playback apparatus using the light emitting device shown inFIG. 4.

FIG. 11 is a cross section showing the construction of a light emittingdevice according to a second embodiment of the invention.

FIGS. 12A and 12B are cross sections for explaining a method ofmanufacturing a light emitting device shown in FIG. 11.

FIGS. 13A and 13B are cross sections for explaining a manufacturingprocess subsequent to FIG. 12B.

FIG. 14 is a cross section for explaining a manufacturing processsubsequent to FIG. 13B.

FIG. 15 is a plan view showing a schematic configuration of a displayapparatus using the light emitting device illustrated in FIG. 11.

FIG. 16 is a diagram showing the configuration of a main portion of adriving circuit of the display apparatus illustrated in FIG. 15.

FIG. 17 is a cross section showing the configuration of a light emittingdevice according to a third embodiment of the invention.

FIGS. 18A and 18B are cross sections for explaining a method ofmanufacturing the light emitting device illustrated in FIG. 17.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention will be described in detail hereinbelowwith reference to the drawings.

First Embodiment

FIG. 4 shows the sectional structure of a light emitting device 10Aaccording to a first embodiment of the invention. The light emittingdevice 10A has a supporting base 11, a first light emitting element 20disposed on one face of the supporting; base 11, and a second lightemitting element 30 disposed on the side of the first light emittingelement 20 opposite to the supporting base 11.

The supporting base 11 is made of a metal such as copper (Cu) and servesas a heat sink for dissipating heat generated by the first and secondlight emitting elements 20 and 30. The supporting base 11 iselectrically connected to an external power source (not shown) and alsohas the role of electrically connecting the first light emitting element20 to the external power source.

The first light emitting element 20 is, for example, a semiconductorlaser capable of emitting light having a wavelength of around 400 nm.The first light emitting element 20 has a configuration in which ann-type cladding layer 22, an active layer 23, a degradation preventinglayer 24, a p-type cladding layer 25, and a p-side contact layer 26which are made of a Group III-V compound semiconductor of the nitridesystem are laid one upon another in the order named on a first substrate21 made of a Group III-V compound semiconductor of the nitride system,on the side thereof on which the supporting base 11 is disposed. TheGroup III-V compound semiconductor of the nitride system refers to amaterial containing at least one of Group 3B elements in theshort-period type periodic table and at least nitrogen (N) from Group 5Belements in the short-period type periodic table.

Specifically, the first substrate 21 is made of, for example, n-type GaNdoped with silicon (Si) as an n-type impurity, and its thickness in thedeposition direction (hereinbelow, simply referred to as thickness) is,for example, 80 to 100 μm. GaN is a transparent material in the visibleregion (about 380 to 800 nm). GaN is a material having excellent thermalconductivity as high as about 1.3 W/(cm·K). By using the characteristic,the first substrate 21 functions as a heat sink which dissipates heatgenerated by the second light emitting element 30.

The n-type cladding layer 22 is, for example, 1 μm thick and is made ofn-type AlGaN (for example, Al_(0.08)Ga_(0.92)N) mixed crystal doped withsilicon as an n-type impurity. The active layer 23 is, for example, 30nm thick and has a multiple quantum well structure including a welllayer and a barrier layer made of Ga_(x)In_(1-x)N (where, x≧0) havingdifferent compositions. The active layer 23 functions as a lightemitting portion.

The degradation preventing layer 24 is, for example, 20 nm thick and ismade of p-type AlGaN (such as Al_(0.2)Ga_(0.8)N) mixed crystal dopedwith magnesium (Mg) as a p-type impurity. The p-type cladding layer 25is, for example, 0.7 μm thick and is made of p-type AlGaN (such asAl_(0.08)Ga_(0.92)N) mixed crystal doped with magnesium as a p-typeimpurity. The p-side contact layer 26 is, for example, 0.1 μm thick andis made of p-type GaN doped with magnesium as a p-type impurity.

A part of the p-type cladding layer 25, and the p-side contact layer 26are formed in a narrow strip shape extending in the cavity direction(perpendicular direction to the drawing sheet in FIG. 4) so as toproduce what is called a laser stripe, thereby restricting a current.The p-side contact layer 26 is provided in the center portion in thedirection (direction indicated by the arrow A in FIG. 4) perpendicularto the cavity direction. Side faces of the p-side contact layer 26 and aside of the p-type cladding layer 25 opposite to the degradationpreventing layer 24 are covered with an insulating layer 27 made ofsilicon dioxide (SiO₂) or the like. The region in the active layer 23corresponding to the p-side contact layer 26 is a light emitting region.

On the side of the p-side contact layer 26 opposite to the p-typecladding layer 25, a p-side electrode 28 is formed. The p-side electrode28 is formed by depositing palladium (Pd), platinum (Pt) and gold (Au)in order from the p-side contact layer 26 side and is electricallyconnected to the p-side contact layer 26. The p-side electrode 28 isalso electrically connected to the supporting base 11 via an adhesivelayer 12. The adhesive layer 12 is made of, for example, an alloy ofgold (Au) and tin (Sn), or tin.

On the side of the first substrate 21 opposite to the supporting base11, an n-side electrode 29 is provided in correspondence with a lasingportion 50, which will be described hereinlater. The n-side electrode 29is obtained by, for example, depositing titanium (Ti) and aluminum inorder from the first substrate 21 side and alloying the depositedmaterials by heat treatment, and is electrically connected to the firstsubstrate 21. The n-side electrode 29 also has the function as a wirefor connecting the lasing portion 50 to the external power source. Onthe side of the first substrate 21 opposite to the supporting base 11, awiring layer 13 for electrical connection to a lasing portion 40 of thesecond light emitting element 30 is formed with an insulating film 14 inbetween. The wiring layer 13 is made of, for example, a metal. Detailsof the lasing portion 40 will be given hereinlater.

Further, a pair of side faces at the ends in the cavity direction of thefirst light emitting element 20 serve as two end planes of the cavity. Apair of reflecting mirror films (not shown) are formed on the pair ofend planes of the cavity. One of the pair of reflecting mirror films isset so as to reflect light produced in the active layer 23 at highreflectance, and the other film is set to reflect light at reflectancelower than the above reflectance, so that light goes out from the otherfilm.

The second light emitting element 30 has, for example, a secondsubstrate 31, the lasing portion 40 and the lasing portion 50. Thelasing portion 40 is capable of emitting light in the range of the orderof 700 nm (for example, 780 nm) and is formed on the second substrate 31on the side thereof on which the supporting base 11 is disposed, with abuffer layer 32 in between. The lasing portion 50 is capable of emittinglight in the range of the order of 600 nm (for example, 650 nm) and isformed on the second substrate 31 on the side thereof on which thesupporting base 11 is disposed, with the buffer layer 32 in between. Thesecond substrate 31 is, for example, about 100 μm thick and is made ofn-type GaAs doped with silicon as an n-type impurity. The buffer layer32 is, for example, 0.5 μm thick and is made of n-type GaAs doped withsilicon as an n-type impurity. The lasing portions 40 and 50 aredisposed with a space of, for example, about 200 μm or less so thattheir cavity directions are aligned with that of the first lightemitting element 20 and the p-side contact layer 26 in the first lightemitting element 20 is positioned between the lasing portions 40 and 50.Specifically, the space between a light emitting region of the lasingportion 40 and a light emitting region of the lasing portion 50 is about120 μm, and the light emitting region of the first light emitting device20 is positioned just in the middle of the light emitting regions of thelasing portions 40 and 50. Details of the light emitting regions of thelasing portions 40 and 50 will be given later.

The lasing portion 40 has a configuration in which an n-type claddinglayer 41, an active layer 42, a p-type cladding layer 43, and a p-typecap layer 44 are laid one upon another in the order named from thesecond substrate 31 side. Each of the layers is made of, for example, aGroup III-V compound semiconductor containing at least gallium (Ga) fromGroup 3B elements in the short-period type periodic table and at leastarsenide (As) from Group 5B elements in the short-period type periodictable.

Specifically, the n-type cladding layer 41 is, for example, 1.5 μm thickand is made of n-type AlGaAs mixed crystal doped with silicon as ann-type impurity. The active layer 42 is, for example, 40 nm thick andhas a multiple quantum well structure including a well layer and abarrier layer made of Al_(x)Ga_(1-x)As (where, x≧0) having differentcompositions. The active layer 42 functions as a light emitting portionand the wavelength of the output light is, for instance, in the range ofthe order of 700 nm. The p-type cladding layer 43 is, for example, 1.5μm thick and is made of p-type AlGaAs mixed crystal doped with zinc as ap-type impurity. The p-type cap layer 44 is, for example, 0.5 μm thickand is made of p-type GaAs doped with zinc as a p-type impurity.

A part of the p-type cladding layer 43, and the p-type cap layer 44 areformed in a narrow strip shape extending in the cavity direction,thereby restricting a current. On both sides of the strip portion,current block regions 45 are provided. The region of the active layer 42corresponding to the p-side cap layer 44 serves as a light emittingregion.

On the side of the p-type cap layer 44 opposite to the p-type claddinglayer 43, a p-side electrode 46 is formed. The p-side electrode 46 isformed by, for example, depositing titanium, platinum and gold in orderfrom the side of the p-side cap layer 44 and alloying the depositedmaterials by heat treatment, and is electrically connected to the p-typecap layer 44. The p-side electrode 46 is also electrically connected tothe wiring layer 13 via an adhesive layer 15. The adhesive layer 15 ismade of, for example, a material similar to that of the adhesive layer12.

The lasing portion 50 has a configuration in which an n-type claddinglayer 52, an active layer 53, a p-type cladding layer 54, and a p-typecap layer 55 are laid one upon another in the order named from the sideof the second substrate 31, with a buffer layer 51 in between. Each ofthe layers is made of, for example, a Group III-V compound semiconductorcontaining at least indium (In) from Group 3B elements in theshort-period type periodic table and at least phosphorus (P) from Group5B elements in the short-period type periodic table.

Specifically, the buffer layer 51 is, for example, 0.5 μm thick and ismade of n-type InGaP mixed crystal doped with silicon as an n-typeimpurity. The n-type cladding layer 52 is, for example, 1.5 μm thick andis made of n-type AlGaInP mixed crystal doped with silicon as an n-typeimpurity. The active layer 53 is, for example, 35 nm thick and has amultiple quantum well structure including a well layer and a barrierlayer made by Al_(x)Ga_(y)In_(1-x-y)P (where x≧0 and y≧0) havingdifferent compositions. The active layer 53 functions as a lightemitting portion. The p-type cladding layer 54 is, for example, 1.0 μmthick and is made of p-type AlGaInP mixed crystal doped with zinc as ap-type impurity. The p-type cap layer 55 is, for example, 0.5 μm thickand is made of p-type GaAs doped with zinc as a p-type impurity.

A part of the p-type cladding layer 54 and the p-type cap layer 55 areformed in a narrow strip shape to produce a current-restricting areaextending in the cavity direction. On both sides of the strip portion,current block regions 56 are provided. The region of the active layer 53corresponding to the p-side cap layer 55 serves as a light emittingregion.

On the side of the p-type cap layer 55 opposite to the p-type claddinglayer 54, a p-side electrode 57 is provided. The p-side electrode 57 iselectrically connected to the p-type cap layer 55 and has, for example,the configuration similar to that of the p-side electrode 46. The p-sideelectrode 57 is also electrically connected to the n-side electrode 29of the first light emitting element 20 via an adhesive layer 16 made ofa material similar to that of the adhesive layer 15.

On the side of the second substrate 31 opposite to the supporting base11, an n-side electrode 33 of the lasing portions 40 and 50 is formed.The n-side electrode 33 is obtained by, for example, depositing an alloyof gold and germanium (Ge), nickel, and gold in order from the side ofthe second substrate 31 and alloying the deposited materials by heattreatment.

Further, a pair of side faces at the ends in the cavity direction of thesecond light emitting element 30 serve as two end planes of the cavity.A pair of reflecting mirror films (not shown) are formed on the pair ofend faces of the cavity of each of the lasing portions 40 and 50. Therelation of reflectance between the pairs of reflecting mirror films isset so as to correspond to that between the pair of reflecting mirrorfilms provided in the first light emitting element 20. Light is emittedfrom the same side of the first light emitting element 20 and the lasingportions 40 and 50 of the second light emitting element 30.

The light emitting device 10A having such a configuration is, forexample as shown in FIG. 5, enclosed in a package 1 for practical use.The package 1 has, for example, a disk-shaped supporting body 2 and acover body 3 provided on the side of one face of the supporting body 2.Inside the cover body 3, the supporting base 11 is supported by thesupporting body 2 and the light emitting device 10A is enclosed. Lightemitted from the light emitting device 10A goes out from a window 3 a ofthe cover body 3.

The package 1 is provided with a plurality of conductive pins 4 a to 4d, and the pin 4 a is electrically connected to the supporting base 11.The other pins 4 b to 4 d, for example, penetrate the supporting body 2via insulating rings 5 b to 5 d respectively and extend from the insideof the cover body 3 to the outside. The wiring layer 13 is electricallyconnected to the pin 4 b via a wire 6 b. The n-side electrode 29 iselectrically connected to the pin 4 c via a wire 6 c. The n-sideelectrode 33 is electrically connected to the pin 4 d via a wire 6 d.Although the package 1 having the four pins 4 a to 4 d is described hereas an example, the number of pins can be set as appropriate. Forexample, when the wiring layer 13 and the supporting base 11 areconnected to each other via a wire, the pin 4 b is unnecessary and thenumber of pins becomes three.

Such a light emitting device 10A can be manufactured as follows. FIGS.6A to 9B show the manufacturing steps of the method of manufacturing thelight emitting device 10A.

First, as shown in FIG. 6A, for example, the first substrate 21 made ofn-type GaN having a thickness of about 400 μm is prepared. On thesurface of the first substrate 21, the n-type cladding layer 22 made ofn-type AlGaN mixed crystal, the active layer 23 made of InGaN mixedcrystal, the degradation preventing layer 24 made of p-type AlGaN mixedcrystal, the p-type cladding layer 25 made of p-type AlGaN mixedcrystal, and the p-side contact layer 26 made of p-type GaN are grown inorder by MOCVD. At the time of growing each of the layers, thetemperature of the first substrate 21 is adjusted to, for example, 750°C. to 1100° C.

Referring to FIG. 6B, a mask (not shown) is formed on the p-side contactlayer 26. The upper layer portion of each of the p-side contact layer 26and the p-type cladding layer 25 is selectively etched into a narrowstrip shape, and thus the p-type cladding layer 25 is exposed.Subsequently, by using the not-shown mask on the p-side contact layer26, the insulating layer 27 is formed so as to cover the surface of thep-type cladding layer 25 and the side faces of the p-side contact layer26.

After forming the insulating layer 27, on and around the surface of thep-side contact layer 26, for example, palladium, platinum, and gold arevapor-deposited in order, and the p-side electrode 28 is formed.Further, in order to easily cleave the first substrate 21 in a processwhich will be described hereinlater, the rear face side of the firstsubstrate 21 is, for example, lapped and polished so that the thicknessof the first substrate becomes about 100 μm.

Subsequently, on the rear face side of the first substrate 21, theinsulating film 14 is formed in correspondence with the position of thelasing portion 40, and the wiring layer 13 is formed on the insulatingfilm 14. In correspondence with the position of the lasing portion 50,for example, titanium and aluminum are vapor-deposited in order, and then-side electrode 29 is formed. Specifically, each of the wiring layer 13and the n-side electrode 29 is formed in a position apart from thep-side contact layer 26 by about 60 μm. In the embodiment, the firstsubstrate 21 is made of GaN which is transparent in the visible region,and layers which are made of Group III-V compound semiconductors and arealso transparent in the visible region are stacked on the firstsubstrate 21. Therefore, the position of the p-side electrode 28 can beobserved from the first substrate 21 side and the positioning in thelithography process can be performed with high precision. That is, thepositions in which the wiring layer 13 and the n-side electrode 29 areformed can be precisely controlled. Since GaN of the first substrate 21is hard, even when the thickness of the first substrate 21 is about 100μm, there is no possibility that the first substrate 21 is cracked orthe like in the lithography process.

After forming the wiring layer 13 and the n-side electrode 29, heattreatment is performed to thereby alloy the n-side electrode 29. Afterthat, although not shown, the first substrate 21 is, for example,cleaved perpendicular to the longitudinal direction of the p-sideelectrode 28 in a predetermined width and a pair of reflecting mirrorfilms are formed on the cleaved faces. In such a manner, the first lightemitting element 20 is fabricated.

As shown in FIG. 7A, for example, the second substrate 31 made of n-typeGaAs having a thickness of about 350 μm is prepared. On the surface ofthe second substrate 31, the buffer layer 32 made of n-type GaAs, then-type cladding layer 41 made of n-type AlGaAs mixed crystal, the activelayer 42 made of Al_(x)Ga_(1-x)As (where x≧0) mixed crystal, the p-typecladding layer 43 made of p-type AlGaAs mixed crystal, and the p-typecap layer 44 made of p-type GaAs are grown in order by MOCVD. At thetime of growing each of the layers, the temperature of the secondsubstrate 31 is adjusted to, for example, 750° C. to 800° C.

As shown in FIG. 7B, a resist film R₁ is formed on the p-type cap layer44 in correspondence with the region in which the lasing portion 40 isto be formed. After that, by using the resist film R₁ as a mask, thep-type cap layer 44 is selectively removed by using, for example,sulfuric-acid-based etchant, and the portion which is not covered withthe resist film R₁ of the p-type cap layer 44, p-type cladding layer 43,active layer 42, and n-type cladding layer 41 is selectively removed byusing hydrofluoric-acid-based etchant. After that, the resist film R₁ isremoved.

Subsequently, as shown in FIG. 8A, by MOCVD for example, the bufferlayer 51 made of n-type InGaP mixed crystal, the n-type cladding layer52 made of n-type AlGaInP mixed crystal, the active layer 53; made ofAl_(x)Ga_(y)In_(1-x-y)P (where x≧0 and y≧0) mixed crystal, the p-typecladding layer 54 made of p-type AlGaInP mixed crystal, and the p-typecap layer 55 made of p-type GaAs are grown in order. At the time ofgrowing each of the layers, the temperature of the second substrate 31is adjusted to, for example, about 680° C.

After that, as shown in FIG. 8B, a resist film R₂ is formed on thep-type cap layer 55 in correspondence with the region in which thelasing portion 50 is to be formed. By using the resist film R₂ as amask, the p-type cap layer 55 is selectively removed by using, forexample, sulfuric-acid-based etchant, and the p-type cladding layer 54,active layer 53, and n-type cladding layer 52 are selectively removed byusing phosphoric-acid-based etchant and hydrochloric-acid-based etchant.The buffer layer 51 is selectively removed by usinghydrochloric-acid-based etchant. After that, the resist film R₂ isremoved.

After removing the resist film R₂, as shown in FIG. 9A, for example, anarrow strip-shaped mask (not shown) is formed on the p-type cap layers44 and 55, and an n-type impurity such as silicon is introduced into thep-type cap layers 44 and 55 and an upper layer portion of the p-typecladding layers 43 and 54 by ion implantation. The impurity introducedregions are insulated and become the current block regions 45 and 56. Inthis case, since the positions of the p-type cap layers 44 and 55 aredefined by using lithography, the positions can be controlledaccurately.

After forming the current block regions 45 and 56, as shown in FIG. 9B,for example, nickel, platinum, and gold are vapor-deposited in order onand around the p-type cap layers 44 and 55 to form the p-side electrodes46 and 57. Further, by lapping and polishing the rear face side of thesecond substrate 31, the thickness of the second substrate 31 is set to,for example, about 100 μm. Subsequently, for example, an alloy of goldand germanium, nickel, and gold are vapor-deposited in order on the rearface side of the second substrate 31 to thereby form the n-sideelectrode 33 common to the lasing portions 40 and 50. After that, heattreatment is performed to alloy the p-side electrodes 46 and 57 and then-side electrode 33. Further, although not shown, for example, thesecond substrate 31 is cleaved in predetermined width perpendicular tothe longitudinal direction of the p-side electrodes 46 and 57 and a pairof reflecting mirror films are formed on the cleaved faces. In such amanner, the second light emitting element 30 is formed.

After forming the first and second light emitting elements 20 and 30 asdescribed above, the supporting base 11 is prepared. For example, by theadhesive layer 12, the insulating layer 27 and the p-side electrode 28of the first light emitting element 20 and the supporting base 11 areattached to each other. For example, by the adhesive layer 15, thep-side electrode 46 of the second light emitting element 30 and thewiring layer 13 are attached to each other. For example, by the adhesivelayer 16, the p-side electrode 57 in the second light emitting element30 and the p-side electrode 29 in the first light emitting element 20are attached to each other. In such a manner, the light emitting device10A shown in FIG. 4 is completed.

Since the second light emitting element 30 is disposed on the firstlight emitting element 20 so as to make the wiring layer 13 and then-side electrode 29 formed with high positioning accuracy by using ahigh-precision lithography technique correspond to the p-type caplayers. 44 and 55 similarly formed with high positioning accuracy byusing a high-precision lithography technique, the positions of the lightemitting regions are also accurately controlled.

In the case of simultaneously attaching the supporting base 11 to thefirst light emitting element 20, and attaching the, first and secondlight emitting elements 20 and 30, it is preferable to form the adhesivelayers 12, 15 and 16 by using the same material. In the case ofperforming adhesion separately, it is preferable to form an adhesivelayer to be attached first by using a material having a melting pointhigher than that of a material of an adhesive layer to be attachedlater. Specifically, the adhesive layer to be attached first is made ofan alloy of gold and tin, and the adhesive layer to be attached later ismade of tin. Thus, the adhesion can be excellently performed in each ofthe times without heating the layers more than necessary.

The light emitting device 10A is enclosed in the package 1 as shown inFIG. 5 and operates as follows.

In the light emitting device 10A, when a voltage is applied between then-side electrode 29 and the p-side electrode 28 in the first lightemitting element 20 via the pins 4 c and 4 a of the package 1, a currentis passed to the active layer 23, light is emitted by recombination ofelectrons and holes, and light having a wavelength of around 400 nm isemitted from the first light emitting element 20. When a predeterminedvoltage is applied between the n-side electrode 33 in the second lightemitting element 30 and the p-side electrode 46, a current is passed tothe active layer 42, light is emitted by recombination of electrons andholes, and light having a wavelength in the band on the order of 700 nmis emitted from the lasing portion 40. Further, when a predeterminedvoltage is applied between the n-side electrode 33 in the second lightemitting element 30 and the p-side electrode 57 via the pins 4 d and 4c, a current is passed to the active layer 53, light is emitted byrecombination of electrons and holes, and light having a wavelength inthe band on the order of 600 nm is emitted from the lasing portion 50.The light goes out from the package 1 through the light outgoing window3 a of the package 1.

Although heat is also generated at the time of light emission, since thefirst substrate 21 is made of a material having relatively high thermalconductivity, the heat generated by the lasing portion 40 or 50 ispromptly dissipated via the first substrate 21 and the supporting base11. The heat generated by the first light emitting element 20 ispromptly dissipated via the supporting base 11.

In the light emitting device 10A according to the embodiment asdescribed above, the first and second light emitting elements 20 and 30are stacked. It becomes therefore unnecessary to grow Group III-Vcompound semiconductor layers of the nitride system, and Group III-Vcompound semiconductor layers of the systems AlGaAs and AlGaInP on thesame substrate. Thus, the multiple-wavelength laser having a wavelengthof around 400 nm can be easily obtained. The use of the light emittingdevice 10A makes it possible to easily produce, for example, an opticaldisk drive capable of optical recording/playback using any optical diskby a plurality of kinds of light sources.

Especially, the first light emitting element 20 has a Group III-Vcompound semiconductor layer of the nitride system so as to emit lighthaving a wavelength of around 400 nm. Thus, by mounting the lightemitting device 10A on an optical device such as an optical disk drive,optical recording/playback using an optical disk on which information isrecorded at higher recording area density becomes possible.

Since the first substrate 21 is made of the material which istransparent in the visible region, the n-side electrode 29 and thewiring layer 13 can be formed with high positioning accuracy by usingthe lithography technique. By attaching the p-side electrodes 46 and 57in the second light emitting element 30 formed with high positioningaccuracy by using the lithography technique, the positions of the lightemitting regions of the first and second light emitting elements 20 and30 can be accurately controlled. Further, by setting each of theintervals to a predetermined small value, light emitted from each of thelight emitting elements is allowed to come out through a region of asmall diameter.

In addition, the first substrate 21 is made of the material having highthermal conductivity, so that the heat generated at the time of lightemission in the lasing portions 40 and 50 can be promptly dissipated tothe supporting base 11 via the first substrate 21. Thus, even when thesecond light emitting element 30 is disposed on the first light emittingelement 20, the temperature of the light emitting element 30 can beprevented from rising, so that the device can stably operate for longtime.

The light emitting device 10A is used for, for example, an optical diskrecording/playback apparatus as an optical device. FIG. 10 schematicallyshows the configuration of the optical disk recording/playbackapparatus. The optical disk recording/playback apparatus reproducesinformation recorded on an optical disk by using light of differentwavelengths and records information onto an optical disk. The opticaldisk recording/playback apparatus has an optical system for guidingoutgoing light L_(out) having a predetermined wavelength emitted fromthe light emitting device 10A to an optical disk D and reading signallight (reflection light L_(ref)) from the optical disk D under thecontrol of the light emitting device 10A and a control unit 111. Theoptical system has a beam splitter 112, a collimator lens 113, a mirror114, a quarter-wave plate 115, an objective lens 116, a signal lightdetection lens 117, a signal light detection photoreceiving device 118,and a signal light reproducing circuit 119.

In the optical disk recording/playback apparatus, the outgoing lightL_(out) having, for example, strong intensity from the light emittingdevice 10 is reflected by the beam splitter 112, made parallel light bythe collimator lens 113, and reflected by the mirror 114. The outgoinglight L_(out) reflected by the mirror 114 passes through thequarter-wave plate 115. After that, the outgoing light L_(out) iscondensed by the objective lens 116, and is incident on the optical diskD, thereby writing information onto the optical disk D. The outgoinglight L_(out) having, for example, weak intensity from the lightemitting device 10 passes through the optical components as describedabove and is incident on and reflected by the optical disk D. Thereflection light L_(ref) passes through the objective lens 116,quarter-wave plate 115, mirror 114, collimator lens 113, beam splitter112, and signal light detection lens 117, and is incident on the signallight detection photoreceiving device 118 where the light is convertedto an electric signal. After that, the information written on theoptical disk D is reproduced by the signal light reproducing circuit119.

As described above, the light emitting device 10A according to theembodiment can be enclosed in a single package and the outgoing lightL_(out) is emitted from the plurality of light emitting regions spacedaccurately. By using the light emitting device 10A, the plurality ofoutgoing light L_(out) of different wavelengths can be guided topredetermined positions by using the common optical system. Thus, thesmall, low-cost optical disk recording/playback apparatus having asimplified configuration can be realized. Since an error in the lightemitting point intervals is extremely small, the position of thereflection light L_(ref) forming an image in a photoreceiving portion(signal light detection photoreceiving device 118) can be prevented fromvarying according to optical disk recording/playback apparatuses. Thatis, the optical system can be easily designed and the yield of theoptical disk recording/playback apparatus can be improved.

The light emitting device 10A of the embodiment can realize lightemission of three wavelengths, that is, around 400 nm, in the range ofthe order of 600 nm, and in the range of the order of 700 nm. Thisenables optical recording/playback by using not only existing variousoptical disks such as CD-ROM (Read Only Memory), CD-R, CD-RW, MD, andDVD-ROM, but also what is called DVD-RAM (Random Access Memory), DVD+RW,DVD−R/RW and the like which are currently proposed as rewritablemass-storage disks. Further, optical recording/playback also becomespossible using next-generation recordable optical disks having higherrecording area density (for example, 20 G bytes or more) (such asoptical disks used for a DVR (Digital Video Recorder) or VDR (Video DiskRecorder) which are proposed as optical disk apparatuses of the nextgeneration). The use of such recordable mass-storage disks of the nextgeneration enables video data recording and reproduction of recordeddata (images) with high picture quality and excellent operability.

The description given above relates to an example in which the lightemitting device 10A is applied to the optical disk recording/playbackapparatus. However, obviously, the light emitting device 10A haveextensive application to various optical apparatuses such as opticaldisk playback apparatuses, optical disk recording apparatuses,magnetooptic disk apparatuses for optical recording/playback usingmagnetooptical disks (MOs), and optical communication systems. It can bealso applied to equipment having a vehicle-mounted semiconductor laserapparatus which has to operate at high temperature, and the like.

Second Embodiment

FIG. 11 shows a sectional structure of a light emitting device 10Baccording to a second embodiment of the invention. The light emittingdevice 10B has the same configuration, action, and effects as those ofthe light emitting device 10A except that a second light emittingelement 60 is provided in place of the second light emitting element 30in the light emitting device 10A in the first embodiment. The samereference numerals are given to the same components as those of thefirst embodiment and their detailed description will not be repeated.

The second light emitting element 60 in the second embodiment has thesame configuration as that of the second light emitting element 30except that a lasing portion 70 capable of emitting light having awavelength in the band on the order of 500 nm (for example, 520 nm) isprovided in place of the lasing portion 40 of the second light emittingelement 30 in the first embodiment and the buffer layer 32 is notprovided.

The lasing portion 70 has a configuration in which, for example, ann-type cladding layer 72, a guide layer 73, an active layer 74, a guidelayer 75, a p-type cladding layer 76, a first p-type semiconductor layer77, a second p-type semiconductor layer 78, a p-type superlattice layer79, and a p-side contact layer 80 are laid one upon another in the ordernamed on the second substrate 31 on the side thereof on which thesupporting base 11 is disposed, with a buffer layer 71 in between. Eachof the layers is made of, for example, a Group II-VI compoundsemiconductor containing at least one element selected from the group ofGroup 2A or 2B elements in the short-period type periodic tableconsisting of zinc (Zn), cadmium (Cd), mercury (Hg), beryllium (Be) andmagnesium (Mg), and at least one element selected from the group ofGroup 6B elements in the short-period type periodic table consisting ofsulfur (S), selenium (Se) and tellurium (Te).

Specifically, the buffer layer 71 is made by depositing in order ann-type GaAs film doped with silicon as an n-type impurity, a ZnSe filmdoped with chlorine (Cl) as an n-type impurity, and a ZnSSe mixedcrystal layer doped with chlorine as an n-type impurity, from the sideof the second substrate 31. The thickness of the buffer layer 71 is, forexample, 100 nm. The n-type cladding layer 72 is, for example, 1 μmthick and is made of n-type ZnMgSSe mixed crystal doped with chlorine asan n-type impurity. The guide layer 73 is, for example, 0.1 μm thick andis made of n-type ZnSSe mixed crystal doped with chlorine as an n-typeimpurity or undoped ZnSSe mixed crystal. The active layer 74 is, forexample, 20 nm thick and has a multiple quantum well structure of a welllayer and a barrier layer which are made of Zn_(x)Cd_(1-x)Se (where x≧0)mixed crystal of different compositions. The active layer 74 functionsas a light emitting portion.

The guide layer 75 is, for example, 0.1 μm thick and is made of p-typeZnSSe mixed crystal doped with nitrogen as a p-type impurity or undopedZnSSe mixed crystal. The p-type cladding layer 76 has, for example, 1.0μm thick and is made of p-type ZnMgSSe mixed crystal doped with nitrogenas a p-type impurity. The first p-type semiconductor layer 77 is, forexample, 0.2 μm thick and is made of p-type ZnSSe mixed crystal dopedwith nitrogen as a p-type impurity. The second p-type semiconductorlayer 78 is, for example, 0.2 μm thick and is made of p-type. ZnSe dopedwith nitrogen as a p-type impurity. The p-type superlattice layer 79 is,for example, 35 nm thick and is formed by alternately depositing ap-type ZnSe film doped with nitrogen as a p-type impurity and a p-typeZnTe film doped with nitrogen as a p-type impurity. The p-side contactlayer 80 is, for example, 0.1 μm thick and is made of p-type ZnTe dopedwith nitrogen as a p-type impurity.

A part of the first p-type semiconductor layer 77, second p-typesemiconductor layer 78, p-type superlattice layer 79, and p-side contactlayer 80 are formed in a narrow strip shape extending in the cavitydirection so that a current is restricted. On both sides of the stripportion, current block regions 81 are provided. The region in the activelayer 74 corresponding to the p-side contact layer 80 serves as a lightemitting region.

On the side of the p-type contact layer 80 opposite to the p-typesuperlattice layer 79, a p-side electrode 82 is formed. The p-sideelectrode 82 is formed by, for example, depositing in order palladium(Pd), platinum, and gold from the side of the p-side contact layer 80and alloying the deposited materials by heat treatment, and iselectrically connected to the p-side contact layer 80. The p-sideelectrode 82 is also electrically connected to the wiring layer 13 viathe adhesive layer 15.

The light emitting device 10B having such a configuration can bemanufactured in a manner similar to the first embodiment except that thesecond light emitting element 60 is formed in place of the second lightemitting element 30 in the light emitting device 10A.

Specifically, the second light emitting element 60 is produced asfollows. First, as shown in FIG. 12A, in a manner similar to the firstembodiment, for example, the buffer layer 51 made of n-type InGaP mixedcrystal, the n-type cladding layer 52 made of n-type AlGaInP mixedcrystal, the active layer 53 made of Al_(x)Ga_(y)In_(1-x-y)P (where x≧0and y≧0) mixed crystal, the p-type cladding layer 54 made of p-typeAlGaInP mixed crystal, and the p-type cap layer 55 made of p-type GaAsare grown in order on the surface of the second substrate 31 made ofn-type GaAs.

Subsequently, as shown in FIG. 12B, in correspondence with the region inwhich the lasing portion 50 is to be formed, a mask M made of silicondioxide or silicon nitride (Si₃N₄) is formed by, for example, CVD(Chemical Vapor Deposition) on the p-type cap layer 55. By using themask M, etching such as RIE (Reactive Ion Etching) is performed, therebyselectively removing the p-type cap layer 55, p-type cladding layer 54,active layer 53, n-type cladding layer 52, and buffer layer 51.

Subsequently, as shown in FIG. 13A, on the surface of the secondsubstrate 31, by MBE (Molecular Beam Epitaxy) for example, the bufferlayer 71 in which an n-type GaAs film, an n-type ZnSe film, and ann-type ZnSSe mixed crystal layer are deposited in the order named, then-type cladding layer 72 made of n-type ZnMgSSe mixed crystal, the guidelayer 73 made of n-type ZnSSe mixed crystal, the active layer 74 made ofZn_(x)Se_(1-x)Cd (where x≧0) mixed crystal, the guide layer 75 made ofp-type ZnSSe mixed crystal, the p-type cladding layer 76 made of p-typeZnMgSSe mixed crystal, the first p-type semiconductor layer 77 made ofp-type ZnSSe mixed crystal, the second p-type semiconductor layer 78made of p-type ZnSe, the p-type superlattice layer 79 in which a p-typeZnSe film and a p-type ZnTe film are alternately deposited, and thep-side contact layer 80 made of p-type ZnTe are grown in order. At thetime of growing each of the layers, the temperature of the secondsubstrate 31 is adjusted to, for example, about 280° C. After that, themask M is removed.

After removing the mask M, as shown in FIG. 13B, for example, a mask(not shown) having an opening corresponding to the region in which thecurrent block region 56 is to be created is formed, and an n-typeimpurity such as chlorine is introduced by ion implantation, therebyforming the current block regions 56. A mask (not shown) having anopening corresponding to the region in which the current block region 81is to be created is formed on the entire surface, and an n-type impuritysuch as chlorine is introduced by ion implantation to the p-side contactlayer 80, p-type superlattice layer 79, second p-type semiconductorlayer 78, and to the upper layer portion of the first p-typesemiconductor layer 77, thereby forming the current block region 81.Since the lithography technique is used here in a manner similar to thefirst embodiment the positions of the light emitting regions in thelasing portions 50 and 70 can be precisely defined.

After forming the current block regions 56 and 81, as shown in FIG. 14,on and around the surface of the p-type cap layer 55, for example,titanium, platinum, and gold are vapor-deposited in order, to therebyform the p-side electrode 57. On and around the surface of the p-sidecontact layer 80, for example, palladium, platinum, and gold arevapor-deposited in order, to form the p-side electrode 82. Subsequently,a mask (not shown) is formed in correspondence with the region in whichthe lasing portions 50 and 70 are formed, and the portion from thep-side contact layer 80 to the buffer layer 71 is selectively removed.

After selectively removing the portion from the p-side contact layer 80to the buffer layer 71, the rear face side of the second substrate 31is, for example, lapped and polished to form the n-side electrode 33 onthe rear face side of the second substrate 31 in a manner similar to thefirst, embodiment. Subsequently, heat treatment is performed to alloythe p-side electrodes 57 and 82 and the n-side electrode 33. Finally,the second substrate 31 is cleaved in a predetermined widthperpendicularly to the longitudinal direction of the p-side electrodes57 and 82, and a pair of not-shown reflecting mirror films are formed onthe cleaved faces. In such a manner, the second light emitting element60 is fabricated.

Since the light emitting device 10B according to the embodiment has thefirst light emitting element 20 capable of emitting light in the band onthe order of 400 nm and the second light emitting element 60 having thelasing portion 70 capable of emitting light in the band on the order of500 nm and the lasing portion 50 capable of emitting light in the rangeof the order of 700 nm, the light emitting device for emitting light ofthree primary colors of red (R), green (G), and blue (B) can berealized. The light emitting device 10B can be used as a light source ofnot only the optical disk drive but also full-color displays.

In the case of using the light emitting device 10B as light sources offull-color displays, by adjusting the composition of the material ofeach of the active layers 23, 53, and 74 as appropriate, light emittedfrom each of the light emitting portions can have a desired hue.

FIG. 15 shows a schematic configuration of a display 120 using the lightemitting device 10B according to the embodiment. The display 120 has aboard 121 and a plurality of light emitting devices 10B according to theembodiment provided on one face of the board 121. For example, each ofthe light emitting devices 10B is enclosed in the package 1 as shown inFIG. 5 and the light emitting devices 10B are arranged in a matrix of Mrows and N columns (where, M and N are natural numbers). Although notshown in FIG. 15, on the board 121, common lines 122 and 123 in thecolumn direction and common lines 124 and 125 in the row direction areformed.

FIG. 16 shows a schematic configuration of a driving circuit of thedisplay 120. The supporting base 11 of each of the light emittingdevices 10B is connected to the common line 122 in the column directionvia a wire, and the n-side electrode 33 in the second light emittingelement 60 is connected to the common line 123 in the column directionvia a wire. The wiring layer 13 is connected to the common line 124 inthe row direction, and the n-side electrode 29 in the first lightemitting element 20 is connected to the common line 125 in the columndirection via a wire. The common lines 122 to 125 are connected to acontrol unit (not shown) and a desired color is displayed according to asignal from the control unit.

The light emitting device 10B of the second embodiment acts in a mannersimilar to the light emitting device 10A of the first embodiment exceptthat, when a voltage is applied between the n-side electrode 33 and thep-side electrode 82 via the pins 4 d and 4 b of the package 1 (FIG. 5),a current is passed to the active layer 74, light is emitted byrecombination of electrons and holes, and light having a wavelength inthe band on the order of 500 nm is emitted from the lasing portion 70.

Third Embodiment

FIG. 17 shows a sectional structure of a light emitting device 10Caccording to a third embodiment of the invention. The light emittingdevice 10C has the same configuration, action, and effects as those ofthe light emitting device 10A of the first embodiment except that afirst light emitting element 90 is provided in place of the first lightemitting element 20 in the light emitting device 10A of the firstembodiment, and a supporting base 17 is provided in place of thesupporting base 11. The same reference numerals are given to the samecomponents as those of the first embodiment and their detaileddescription will not be repeated here.

The first light emitting element 90 is largely different from the firstlight emitting element 20 with respect to the point that a differentmaterial is used for a first substrate 91. For example, the firstsubstrate 91 is made of sapphire having a thickness of about 80 μm.Sapphire is an insulating material and is transparent in the visibleregion like GaN. The first light emitting element 90 has a configurationin which, for example, on the c-cut plane of the first substrate 91; ann-side contact layer 93, the n-type cladding layer 22, the active layer23, the degradation preventing layer 24, the p-type cladding layer 25,and the p-type contact layer 26 are laid one upon another in the ordernamed from the side of the first substrate 91 with a buffer layer 92 inbetween. The insulating layer 27 is formed on the surface of the p-typecladding layer 25 and the side faces of the p-side contact layer 26, andthe p-side electrode 28 is formed on the side of the p-side contactlayer 26 opposite to the p-side cladding layer 25.

The buffer layer 92 has, for example, 30 nm thick and is made of undopedGaN or n-type GaN doped with silicon as an n-type impurity. The n-sidecontact layer 93 is, for example, 5 μm thick and is made of n-type GaNdoped with silicon as an n-type impurity.

The n-side contact layer 93 has an exposed portion in which the n-typecladding layer 22, the active layer 23, the degradation preventing layer24, the p-type cladding layer 25, and the p-side contact layer 26 arenot formed. In the exposed portion, for example, an n-side electrode 94in which titanium and aluminum are deposited in order from the side ofthe n-side contact layer 93 and alloyed by heat treatment is formed. Inthe embodiment, the insulating film 27 is provided so as to cover alsothe side faces of the p-type cladding layer 25, degradation preventinglayer 24, active layer 23, and cladding layer 22.

The supporting base 17 is made of an insulating material having highthermal conductivity such as aluminum nitride (AlN). On one face of thesupporting base 17, a wiring layer 17 a made of a metal is provided incorrespondence with the p-side electrode 28 in the first light emittingelement 90, and a wiring layer 17 b made of a metal is provided incorrespondence with the n-side electrode 94. The p-side electrode 28 andthe wiring layer 17 a are attached to each other with the adhesion layer12 in between, and the n-side electrode 94 and the wiring layer 17 b areattached to each other with an adhesion layer 18 in between.

On the side of the first substrate 91 opposite to the supporting base17, the wiring layer 13 is provided in a manner similar to the firstembodiment, and a wiring layer 19 made of a metal is provided forconnecting the lasing portion 50 to the external power source isprovided in place of the n-side electrode 29 in the first embodiment.

The light emitting device 10C is used by, for example, being enclosed ina package in a manner similar to the first embodiment. In the package, aplacement stage is provided on one face of the supporting body, and thesupporting base 17 is placed on the placement stage. The package has,for instance, five pins which are electrically connected to the wiringlayers 13, 17 a, 17 b, and 19 and the n-side electrode 33 via wires. Inthis case as well, the number of pins can be set as appropriate in amanner similar to the first embodiment.

The light emitting device 10C can be manufactured as follows.

First, as shown in FIG. 18A, for example, the first substrate 91 made ofsapphire having a thickness of about 400 μm is prepared. On the c-cutplane of the first substrate 91, the buffer layer 92 made of undoped GaNor n-type GaN is grown. At this time, the temperature of the firstsubstrate 91 is set to, for example, 500° C. Subsequently, on the bufferlayer 92, the n-type contact layer 93 made of n-type GaN, the n-typecladding layer 22 made of n-type AlGaN mixed crystal, the active layer23 made of InGaN mixed crystal, the degradation preventing layer 24 madeof p-type AlGaN mixed crystal, the p-type cladding layer 25 made ofp-type AlGaN mixed crystal, and the p-side contact layer 26 made ofp-type GaN are grown in order. At the time of growing each of thelayers, the temperature of the first substrate 91 is adjusted to anappropriate temperature, for example, from 750 to 1100° C.

As shown in FIG. 18B, the p-side contact layer 26, p-type cladding layer25, degradation preventing layer 24, active layer 23, and n-typecladding layer 22 are etched in order; to expose a part of the n-sidecontact layer 93. After that, a not-shown mask is formed and, by usingthe mask, the upper layer portion in the p-type cladding layer 25, andthe p-side contact layer 26 are formed in a narrow strip shape by, forexample, RIE.

The insulating layer 27 made of silicon dioxide is formed on the sidefaces of the layers of which part is selectively etched and on thesurface of the p-type cladding layer 25 by, for example, vapordeposition. After that, the rear face side of the first substrate 91 islapped and polished so that the thickness of the first substrate 91becomes, for example, about 100 μm.

After thinning the first substrate 91, on the side of the firstsubstrate 91 opposite to the buffer layer 92, the wiring layers 13 and19 are formed in predetermined positions. In a manner similar to thefirst embodiment, the first substrate 91 is made of the materialtransparent in the visible region, so that the positions in which thewiring layers 13 and 19 are formed can be precisely controlled.

Subsequently, for instance, nickel, platinum, and gold arevapor-deposited in order on and around the surface of the p-side contactlayer 26 to form the p-side electrode 28. For example, titanium andaluminum are vapor-deposited in order on the surface of the n-sidecontact layer 93 to thereby form the n-side electrode 94. Further, byconducting heat treatment, the p-side electrode 28 and the n-sideelectrode 94 are alloyed. After that, though not shown here, the firstsubstrate 91 is, for example; cleaved in a predetermined widthperpendicular to the longitudinal direction of the p-side electrode 28,and a pair of reflecting mirror films are formed on the cleaved faces.In such a manner, the first light emitting element 90 is fabricated.

After that, in a manner similar to the first embodiment, the secondlight emitting element 30 is fabricated.

The supporting base 17 on which wiring layers 17 a and 17 b are formedis prepared, the p-side electrode 28 in the first light emitting element90 and the wiring layer 17 a are attached to each other with theadhesive layer 12 in between, and the n-side electrode 94 and the wiringlayer 17 b are attached to each other with the adhesive layer 18 inbetween. The p-side electrode 46 in the second light emitting element 30and the wiring layer 13 are attached to each other with the adhesivelayer 15 in between, and the p-side electrode 57 and the wiring layer 19are attached to each other with the adhesive layer 16 in between. Insuch a manner, the light emitting device 10C is completed.

In the light emitting device 10C according to the embodiment, the firstsubstrate 91 is made of sapphire which is transparent in the visibleregion, so that the light emitting regions of the first and second lightemitting elements 90 and 30 can be precisely controlled in a mannersimilar to the first embodiment.

Although the invention has been described above by the embodiments, theinvention is not limited to the embodiments but can be variouslymodified. In the foregoing embodiments, the specific stacked structuresof the first light emitting elements 20 and 90 and the second lightemitting elements 30 and 60 have been described as examples. Theinvention is similarly applied to the case where the first lightemitting elements 20 and 90 or second light emitting elements 30 and 60have other structures. For example, the first light emitting element mayhave a construction to restrict a current by current block regions in amanner similar to the second light emitting elements 30 and. 60. Thesecond light emitting element may have a construction to narrow acurrent by an insulating film made of silicon dioxide or the like in amanner similar to the first light emitting elements 20 and 90. Althougha ridge-guiding type semiconductor laser in which gain-guiding type andrefractive index-guiding type are combined has been described as anexample in the foregoing embodiments, the invention can be similarlyapplied to a gain-guiding type semiconductor laser and a refractiveindex-guiding type semiconductor laser.

Further, in the foregoing embodiments, the case where the layers made ofGaN, AlGaAs, and AlGaInP compounds are formed by MOCVD has beendescribed. The layers may be formed by other vapor phase epitaxy such asMBE or hydride vapor phase epitaxy. The hydride vapor phase epitaxy isvapor phase epitaxy in which halogen contributes to transport orreaction. Although the case where the layers made of ZnSe compounds areformed by MBE has been described in the second embodiment, the layersmay be formed by other phase vapor epitaxy such as MOCVD.

In addition, although the specific examples regarding the materials ofthe first substrates 21 and 91 in the first light emitting elements 20and 90 have been described, other materials may be also used. It ispreferable to use a material which is transparent in the visible region,since effects described in the foregoing embodiments are obtained. Morepreferably, a material having high thermal conductivity is used.Examples of such materials are aluminum nitride and silicon carbide(SiC).

Further, in the third embodiment, the case where the second lightemitting element 30 having the lasing portion 40 of the system AlGaAsand the lasing portion 50 of the system AlGaInP is provided has beendescribed. Alternatively, the second light emitting element 60 describedin the second embodiment may be provided.

Further, in the foregoing embodiments, the case where the first lightemitting element 20 (90) and the second light emitting element 30 (60)emit light of different wavelengths has been described. A plurality ofthe first light emitting element 20 (90) can be stacked on one face ofthe supporting base 11 (17). Further, a plurality of light emittingelements of different characteristics or structures can be stacked. Inthis case, the wavelengths may be the same or different from each other.In the case of stacking a plurality of light emitting elements ofdifferent characteristics, for example, a low-output device and ahigh-output device can be mixedly used.

Although the case where the first light emitting element 20 (90) has onelight emitting portion has been described in the foregoing embodiments,the first light emitting element 20 (90) may have a plurality of lightemitting portions, specifically, a plurality of lasing portions in amanner similar to the second light emitting element 30. In this case,the wavelengths of the lasing portions may be the same or different fromeach other. The characteristics or structures may be the same ordifferent from each other.

Further, in the embodiments, the case where the second light emittingelement 30 (60) has two lasing portions has been described. The numberof the lasing portions of the second light emitting element may be oneor three or more. The wavelengths, characteristics, or structures of thelasing portions may be the same or different from each other.

In addition, although the case where each of the second light emittingelements 30 and 60 is what is called a monolithic typemultiple-wavelength laser has been described in the foregoingembodiments, the invention can be also applied to the case where thesecond light emitting element is what is called a hybrid typemultiple-wavelength laser as shown in FIG. 2.

Further, although the specific examples regarding the materials of thesupporting bases 11 and 17 have been described in the foregoingembodiments, other materials may be also used. However, a materialhaving high thermal conductivity is preferable. Although the supportingbase 11 is made of a metal in the first and second embodiments, in amanner similar to the third embodiment, the supporting base may be madeof an insulating material and a wire may be provided on the supportingbase.

In addition, although the supporting base 11 (17) is directly supportedby the supporting body 2 at the time of housing the light emittingdevice in the package 1 in the foregoing embodiments, it is alsopossible to provide a placement stage for the supporting body 2 andplace the supporting base 11 (17) on the placement stage.

Although a semiconductor laser has been-described as a specific exampleof the light emitting element in the embodiments, the invention can bealso applied to a light emitting device having other light emittingelement such as a light emitting diode (LED).

According to the light emitting device of the invention, since theplurality of light emitting elements are stacked on one face of thesupporting base, it is unnecessary to dispose a plurality of lightemitting elements on the same substrate, and the device can be easilymanufactured.

Especially, according to the light emitting device of one aspect of theinvention, the first substrate is transparent in the visible region, sothat the positions of the light emitting regions in the first and secondlight emitting elements can be precisely controlled.

Moreover, according to the light emitting device of one aspect of theinvention, the first light emitting element has a semiconductor layercontaining at least one of Group 3B elements and at least nitrogen (N)from Group 5B elements, so that the first light emitting element canemit light of a wavelength around 400 nm. Consequently, when the lightemitting device is mounted on an optical device, an optical devicehaving higher performance can be realized.

Further, according to the light emitting device of one aspect of theinvention, the first substrate is made of either a Group III-V compoundsemiconductor of the nitride system containing at least one of Group 3Belements and at least nitrogen from Group 5B elements, or sapphire. Heatgenerated at the time of light emission in the second light emittingelement can be therefore promptly dissipated via the first substrate.Thus, a temperature rise in the second light emitting element can beprevented and the device can operate stably for long time.

In addition, the optical device according to the invention isconstructed by using the light emitting device of the invention.Consequently, higher performance can be achieved and reduction in sizeand cost can be realized.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

1. A light emitting device comprising: a supporting base withinsulation; a first light emitting element being provided on one face ofthe supporting base, and having a first substrate with insulation, thefirst substrate being transparent in the visible region; and a secondlight emitting element being provided on the side of the first lightemitting element opposite to the supporting base, and having a secondsubstrate.
 2. A light emitting device according to claim 1, wherein thefirst and second light emitting elements can emit light of differentwavelengths.
 3. A light emitting device according to claim 2, whereinthe first light emitting element has a semiconductor layer containing atleast one of Group 3B elements and at least nitrogen (N) from Group 5Belements.
 4. A light emitting device according to claim 1, wherein thefirst substrate is made of either a Group III-V compound semiconductorof the nitride system containing at least one of Group 3B elements andat least nitrogen (N) from Group 5B elements, or sapphire (Al₂O₃).
 5. Alight emitting device according to claim 1, wherein the first lightemitting element has a light emitting portion on the first substrate onthe side thereof on which the supporting base is disposed.
 6. A lightemitting device according to claim 1, wherein the second light emittingelement has a light emitting portion on the second substrate on the sidethereof on which the first light emitting element is disposed.
 7. Alight emitting device according to claim 1, wherein the second lightemitting element has a plurality of light emitting portions of differentoutput wavelengths.
 8. A light emitting device according to claim 7,wherein the second light emitting element has an individual electrodeper each of the plurality of light emitting portions.
 9. A lightemitting device according to claim 1, wherein the second substrate ismade of gallium arsenide (GaAs).
 10. A light emitting device accordingto claim 1, wherein the second light emitting element has asemiconductor layer containing at least gallium (Ga) from Group 3Belements and at least arsenide (As) from Group 5B elements.
 11. A lightemitting device according to claim 1, wherein the second light emittingelement has a semiconductor layer containing at least indium (In) fromGroup 3B elements and at least phosphorus (P) from Group 5B elements.12. A light emitting device according to claim 1, wherein the secondlight emitting element has a semiconductor layer containing at least oneelement selected from the group of Group 2A or 2B elements consisting ofzinc (Zn), cadmium (Cd), mercury (Hg), beryllium (Be) and magnesium(Mg), and at least one element selected from the group of Group 6Belements consisting of sulfur (S), selenium (Se) and tellurium (Te). 13.An optical device having a light emitting device, the light emittingdevice comprising: a supporting base with insulation; a first lightemitting element being provided on one face of the supporting base, andhaving a first substrate with insulation, the first substrate beingtransparent in the visible region; and a second light emitting elementbeing provided on the side of the first light emitting element oppositeto the supporting base, and having a second substrate.
 14. A method ofmanufacturing a light emitting device comprising the steps of: forming afirst light emitting element on a front face of a first substrate withinsulation being transparent in the visible region, and then forming afirst wire on a rear face of the first substrate; bonding the firstlight emitting element formed on the first substrate to a supportingbase with insulation on which a second wire is formed so that the lightemitting element is electrically connected to the second wire; andbonding a second light emitting element having a second substrate to thefirst wire on the first substrate so that the second light emittingelement is electrically connected to the first wire on the firstsubstrate.
 15. An optical device according to claim 13, wherein thefirst light emitting element has a light emitting portion on the firstsubstrate on the side thereof on which the supporting base is disposed.